Generally, when information is recorded on an information medium (hereinafter, called an optical disk) using laser light, tracking control is performed by detecting a positional deviation of a light spot on the optical disk from a desired track using reflected light from the optical disk and by driving an objective lens in accordance with the detection signal so that the light spot can scan on the desired track.
If, however, an optical disk has a dust attached thereon or a defect (hereinafter, generically called a deficiency) in an information layer thereof, the accurate reflected light from the optical disk cannot be obtained, and thus the accurate tracking control is difficult to perform. When a trouble occurs in the tracking control, a problem that laser light is irradiated to the outside of an area to be recorded accordingly may occur.
In order to avoid the above problem, a method for detecting deficiencies on an optical disk from a change in the reflected light has been utilized conventionally. This method makes use of a phenomenon that the amount of the reflected light decreases when a deficiency lies on the optical disk. That is, the deficiencies on the optical disk can be detected by comparing the amount of the reflected light from the optical disk with a predetermined threshold value.
However, when recording information onto the optical disk, an optimum emitting power of a laser light source depends on the temperature of the optical disk or the like, and thus it is necessary to adjust the emitting power of the laser light source to an optimum value at a required time. Meanwhile, when the emitting power of the laser light source changes, the amount of the reflected light from the optical disk accordingly changes. Thus, it was found out that deficiencies on the optical disk were not able to be detected accurately by the conventional configuration for detecting deficiencies on the optical disk, in which the amount of reflected light from the optical disk is compared with the predetermined threshold value.
In light of the above-stated problems, another technique for detecting deficiencies on an optical disk is proposed, which includes the following means: a means for irradiating an information track configured on the optical disk with laser light via an optical system and receiving the reflected light from the information track using a photodetector so as to check the deficiencies on a recording track, thereby detecting average reflected light from the information track; and a detection controlling means for controlling the means for detecting the deficiencies on the information track in accordance with the average reflected light (see, for example, JP60(1985)-107749A, P.3 lower right column line 15-P.4 upper right column line 1, and FIG. 3). Using this technique, the change of the reflected light is detected by assuming the average value of the reflected light as a threshold value. Thus even when the amount of the reflected light changes, the deficiencies on the optical disk can be detected regardless of the amount of the reflected light.
According to the above configuration, however, since the deficiencies on the optical disk are detected using the average reflected light, problems in detecting the deficiencies on the optical disk may occur because of the incapability of responding to the abrupt change of the emitting power of the laser light source, for example, when switching from a reproducing mode to a recording mode. That is, more specifically, when the deficiency is present on the optical disk immediately after the switching from the reproducing mode to the recording mode, it is hard to detect the deficiency, and the tracking control is negatively affected, thereby the light beam is applied to the outside of an area to be recorded.